Trunk piston



May 4, 1937. J. FLAMMANG ET AL TRUNK PI STON Filed May 21, 1934 Patented May 4, 1937 "UNITED STATES ATENT OFFICE TRUNK PISTON John Fianiniang, University City, Percy L. Bowler, St. Louis, and Herman Ernst, Pine Lawn, "Ho a-ignouto The Sterling Corporation, St. Lonia,lilo.,acorporationofneiaware Application May 21, 19:4, Serial No. 726,644

4 cu (cam-14) This invention pertains to trunk pistons, such as are used in internal combustion engines. More particularly it pertains to the type of piston in which the skirt is formed of a metal, such.

skirt.

It has been found that in this type of piston, on account of the play of the piston in the cylinder during operation, there is a pounding action on the skirt, particularly at the head end thereof, which tends to rupturethe metal at that point.

One of the objects of this invention is to provide a piston structure of this type, in which the skirt is re-enforced in a simple and effective manner.

In the manufacture'of this type of piston, the skirt is often constructed of sheet steel drawn or rolled to the proper shape. The drawing or rolling process and apparatus impose certain limitations on the shapes which may be formed without involving prohibitive expense. Some of the preferable shapes of piston skirts involve formations which are diflicult to carry out by these processes.

Another objectof this invention, therefore, is to provide a structure which may be manufactured by simpler operations and, accordingly, at reduced expense.

A source of dimculty in the operation of this type of piston is that the higher rate of expansion of the head metal may impose upon the skirt an excessive expansion under operating temperatures, particularly in that part of the skirt adjacent the ends of the wrist pin.

- Itis another object of this invention, therefore, to provide a structure whereby this portion of the skirt may be relieved of the effect of the expansion of'the head metal to expand the skirt.

Another object of this invention is to provide a piston of simple structure, which may be inexpensive to manufacture and rugged in service. V Further objects will appear from the following description taken in connection with the accompanying drawing, in which Figure 1 is a sectional view of a piston embodying this invention, showing a method of reenforcing the skirt at its upper end;

Figure 2 is a similar view, showing a modified structure for re-enforcing the skirt;

Figure 3 is a similar view, showing another form of structure for this purpose:

Figures 4 and 5 are'detail views showing modifications of the structure' embodying this invention; and

Figure 6 is an enlarged detail of Figure 2, showing a sectional view of the wrist pin boss taken along the wrist pin axis, showing the manner in which the expansion of the head metal is compensated for.

Referringto the drawing, I designates the piston skirt, which may be made of iron or steel,

preferably sheet metal. In the embodiment of Figure 1, the skirt is made of a single piece of metal and is formed with an inwardly extending radial flange 2 and, at the inner edge of said flange, an inwardly tapering conical flange 3.. In casting the head portion 1 of the piston, the skirt is placed in the mold and the head portion cast thereon, so as to imbed the upper portion of the flange 3 in the head metal. The lower limit of the cast metal is positioned so as to form a groove 5 between the head metal and the flange 2 adapted to provide an oil groove and in which an oil scraping ring (not shown) may be mounted. The skirt may be perforated with one or more holes 6 to permit drainage of oil from the groove 5 into the interior of the piston.

In accordance with the embodiment of Figure 1, the skirtis formed of a metal of heavier gauge than is required for the finished skirt. The skirt is then formed so that just below the flange 2 there is an outwardly tapering portion 1, extending downwardlya suitable distance, after which the lower portion of the skirt is formed cylindrically. The original shape of this skirt is indicated in dotted lines in Figure 1. After the head has been cast and during the finishing operations on the piston, the skirt is machined to its final cylindrical form on the line AB. This operation reduces the thickness of the lower portion of the skirt to a fraction of its original thickness, while at the taperedportion 1 the thickness gradually increases up to the flange 2. Accordingly, just below the flange 2, at which portion the maximum strength is required, the wall of the skirt is considerably thicker than at other portions. Accordingly, a re-enforcement is provided so that the extra strength of this portion of the skirt is sufiicient to withstand the pounding action received during operation.

The embodiment shown in Figure 1 is claimed in our co-pending application Serial Number 132,220, filed March 22, 1937 which is a division of this application.

radial flange 2, also similar to that of Figure 1,

and a downwardly extending cylindrical flange i matching the wall of the skirt I and fitted therewithin at the upper end thereof. The flange I0 is welded or otherwise permanently secured to the skirt l around its periphery.

This structure provides re-enforcement at the upper end of the skirt in the arrangement of the flange Hi. This flange being welded to the skirt. provides a double thickness of metal at this point. This assists in stiffening this portion of the skirt and also in increasing its mechanical strength.

It will be noted that the flange 2 is in all cases spaced from the lower surface of the head portion. This provides a portion of the flange 3, which is clear of the cast metal, so that it may flex around the junction of the flanges 2 and 3 in order to accommodate itself to the expansion and contraction of the head metal. It should be understood that when the head is first cast, the metal thereof contracts upon cooling at a greater rate thandoes the iron of the flange 3. Accordingly, this flange is forced to yield under the contraction of the head metal. The flange 2, however, together with the re-enforced portion at the flange 10, provides for stifiemng the upper portion of the skirt against such contraction. Accordingly, the flange 3 must flex, as stated, and the fact that the flange 2 is spaced from the lower limit of the head metal provides a free portion of the flange 3 adapted to accommodate such flexure. This structure has the effect of maintaining the diameter of the upper end of the skirt at the flange 2 very nearly constant while the head portion of the piston expands and contracts under the variation in temperature imposed by operating conditions.

In the embodiments of Figure 3, the section 9 is given a similar form to that of Figure 2, but the flange 3 is somewhat longer so that the flange I0 is connected to the skirt at a point somewhat below the flange 2, which is formed on the skirt proper. In this way the length of the flange 3 can be increased and its point of flexure spaced a greater distance from the piston head. Accordingly, a less stress is imposed on the skirt during expansion and contraction of the head.

In the embodiment of Figure 3, with the flange 2 formed on the skirt I, difliculties are introduced in providing such a flange as the flange 8 of Figure 2. This is on account of the necessity of providing an internal core for the drawing operation, which core must be withdrawn axially from the piston. Such a flange, therefore, interferes with the withdrawal of the core. According to this invention, therefore, a separate flange ring II is provided for the open end of the skirt, and this may be welded or otherwise permanently secured in place, as shown in Figure 3. This structure may also be used for Figure 2.

Referring now more particularly to Figure 6, the wrist pin boss l2 is usually cast directly against the interior surface of the skirt I. In the construction shown, the skirt is perforated at the end of the wrist pin axis so' as to provide an opening through which the pinmay be inserted. The metal of the skirt surrounding this opening is flanged inwardly, as indicated at l3. This flange is formed at an angle to the wrist pin axis. When the boss is first cast and while still at setting temperature, the position of the skirt metal is closely against the castmetal. As the cast metal contracts radially with respect to the wrist pin axis, the flange I3 is forced outwardly by pressure of the contracting metal thereon to the position indicated by the broken lines. This forms a bulge on the surface of the piston at this point. During the flnishing operation, the piston skirt is turned down to the required diameter, and this bulge is turned off, so that the flnal shape is as shown in solid lines. 4 In this condition, a gap I4 is left between the cast metal and the metal of the skirt. Thereafter, when the head metal expands under the increased operating temperature, areverse movement between these parts takes place. The wrist pin boss enlarges in diameter and, accordingly, the skirt metal is permitted to return, taking up the gap- I 4 partly. This induces a tendency for the skirt diameter to contract at this point. However, as

the head portion of the piston expands as a.

It will be seen that this invention provides a Q piston which is not only simple to manufacture, but is protected against most of the undesirable consequences of the uneven relative expansion between the cast head and the iron skirt. The member 9 provides, in effect, a carrier member by which the skirt is carried on the head. This carrier member has a yielding portion imbedded in the head which may accommodate itself to the expansion and contraction of the latter. The skirt itself is relieved of the effects of such expansion and, accordingly, maintains a practically constant diameter under changes of temperature. It will be noted that the flanges l0 are cylindrical so as to match the cylindrical form of the skirt itself. The shape of these'flanges provides for a simple type of apparatus to perform the welding operation, whether this operation is performed before or after casting the head. The skirt is stifiened at its upper end by the flange 2 and also by the re-enforcement of the carrier member. Accordingly, the yielding of the latter.

member is not imposed upon the skirt itself. The structure of the tapered flanges at the wrist pin openings is one very simple to provide as a manufacturing operation and is very effective in compensating for the expansion of the head along the wrist pin axis, a feature which has given great difliculty in prior pistons.

While this piston has been described as a unitary structure, it will be understood that individual features or subcombinations thereof may be used separately without reference to other features or the entire combination. It will also be understood that any desired combination of different features may be embodied in the single structure and that the use of such separate features or combinations is contemplated by-this invention and is within the scope of the appended claims. It is further obvious that various changes may be made, within the scope of the appended .claims, in the details of construction without departing from the spirit oi. this invention. It is to be understood, therefore, that this invention is not limited to the specific details shown and/or described.

Having thus described the invention, what is claimed is:

1. A trunk piston for internal combustion engines, comprising, a skirt of metal having a low rate of thermal expansion, a head of cast metal having a higher rate of thermal expansion, said skirt having a portion cast in said head and a portion engaging the cast metal for movement relatively thereto upon thermal expansion and contraction, and means to direct the forces of engagement to expand said skirt portion upon contraction of said metal, said portion tending to contract upon thermal expansion of the head metal.

2. A trunk piston for internal combustion engines, comprising, a skirt 01' metal having a low rate of thermal expansion, a head of cast metal having a higher rate of thermal expansion and provided with wrist-pin bearings, said skirt having a portion cast in said head and a portion adjacent the end of the wrist pin bearing engaging the cast metal for movement relatively thereto upon thermal expansion and contraction, and means to direct the forces of engagement to expand said skirt portion upon contraction of said metal, said portion tending to contract upon thermal expansion of the head metal.

3. A trunk piston for internal combustion engines, comprising. a skirtof metal having a low rate of thermal expansion provided with an inturned flange at its lower end, a head of cast metal having a higher rate of thermal expansion, and a separate carrier member connecting said head and said skirt having a yielding portion cast in said head and free for flexure to a point spaced from said head and also a portion permanently secured to the upper rim of said skirt.

4. A trunk piston for internal combustion engines, comprising, a skirt of sheet metal having a low rate of thermal expansion, and. a head of cast metal having a higher rate of thermal expansion, said skirt having a separate carrier member provided with a radially directed flange at the upper endthereof but spaced from said head, a yielding connection extending upwardly from said flange and bonded into said head. said carrier having a cylindrical flange portion internally engaging and secured to said skirt.

JOHN FLAMNIANG. PERCY L. BOWSER. HERMAN ERNST. 

